1. Field of the Invention
The present invention relates to a presensitized plate, more specifically to a positive-working type presensitized plate (hereinafter referred to as a positive-working PS plate) having a high sensitivity.
2. Description of the Prior Art
Heretofore, positive-working PS plates which comprise a grained hydrophilic aluminum support having coated thereon a layer containing an orthoquinonediazide compound and a phenol resin have widely been used.
Such positive-working PS plates utilize a property of the orthoquinonediazide compound that it decomposes by irradiation of actinic light to form a five-membered carboxylic acid which is alkali soluble, but have a defect that their sensitivities are inadequate. This defect is based on the fact that in the orthoquinonediazide compound quantum yield does not exceed one essentially.
Trials for enhancing the sensitivity of a light-sensitive composition containing an orthoquinonediazide compound have hitherto been conducted, but it has been very difficult to enhance the sensitivity while maintaining development latitude. Such trials are disclosed, for example, in Japanese Published Examined Patent Application No. 12242/1973, Japanese Published Unexamined Patent Application No. 40125/1977, and U.S. Pat. No. 4,307,173.
Further, several proposals have recently been made as to a light-sensitive composition which acts positively without using an orthoquinonedizaide compound. One of such compositions contains a polymer compound having an orthonitrocarbinol ester group as disclosed in Japanese Published Examined Patent Application No. 2696/1981. However, the sensitivity of the composition is not adequate due to the same reason as in the orthoquinonediazide. Separately, as a process for enhancing the sensitivity of a light-sensitive composition, there is a process for enhancing the sensitivity by using a light-sensitive system which is activated through contact action, more specifically a process which comprises applying a known principle that exposure areas are solubilized by causing a second reaction with the acid which is formed by photolysis.
As the examples of such light-sensitive systems, combinations of a compound which forms an acid by photolysis with other compounds such as an acetal or O,N-acetal compound (Japanese Published Unexamined Patent Application No. 89003/1973), an orthoester or amidoacetal compound (Japanese Published Unexamined Patent Application No. 120714/1976), a polymer having an acetal or ketal group in the principal chain (Japanese Published Unexamined Patent Application No. 133429/1978), an enolether compound (Japanese Published Unexamined Patent Application No. 12995/1980) an N-acyliminocarbonic acid compound (Japanese Published Unexamined Patent Application No. 126236/1980), and a polymer having an orthoester group in the principal chain (Japanese Published Unexamined Patent Application No. 17345/1981) are mentioned. As quantum yields of these light-sensitive systems respectively exceed one, light-sensitive compositions containing these light-sensitive system generally seem to have a high sensitivity. However, the reaction rate of the reaction of an acid as formed by photolysis with an O,N-acetal compound or a polymer having an acetal or ketal group in the principal chain is generally late, a light-sensitive composition containing such a compound does not exhibit an adequate sensitivity in practical use. Further, though a light-sensitive composition containing an orthoester, amidoacetal, enolether or N-acyliminocarbonic acid compound indeed exhibits a high sensitivity, they have poor stability and cannot be preserved over a long period. A light-sensitive composition containing a polymer having an orthoester group in the principal chain also exhibits a high sensitivity, but has only a narrow development latitude in development.
Further, a method for making a lithographic printing plate by applying a layer containing photopolymerizable type microcapsules on a water resistant support, subjecting the applied surface to pattern exposure, pressurizing the surface and re-exposing the surface is disclosed in Japanese Published Unexamined Patent Application No. 224752/1983. The presensitized plate used in this method is highly sensitive and the method is a method wherein a lithographic printing plate is made through a dry treatment by utilizing the hydrophilic property of the microcapsule wall membrane and the lipophilic property of the photopolymerizable type resin. However, the thus obtained lithographic printing plate is inadequate in its hydrophilic property, is liable to form background contamination and has only a poor printing durability. Further, as the lipophilic property of the photopolymerizable type resin is impaired by the hydrophilic property of the microcapsule wall membrane, the lipophilic property of the printing plate is inadequate. As a result, the printing plate has a defect that the concentration of an ink applied thereon cannot be made high.